Method for producing glass precursor compositions and glass compositions therefrom

ABSTRACT

AN IMPROVED PROCESS FOR PREPARING INORGANIC, OXIDIC, GLASS PRECURSOR COMPOSITIONS CORRESPONDING TO A GLASS CONSISTING ESSENTIALLY OF SILICA, BORIC OXIDE, LEAD OXIDE, AND, OPTIONALLY, ALUMINA OR ZINC OXIDE OR MIXTURES OF ALUMINA AND ZINC OXIDE, WHEREIN THE GLASS HAS A SINTERING TEMPERATURE IN THE RANGE OF ABOUT 300*C. TO ABOUT 600* C. AND MELTS TO A UNIFORM GLASS PRODUCT AT A TEMPERATURE OF LESS THAN ABOUT 860*C. BY A PROCESS WHEREIN A CLEAR SOLUTION OF A FURTHER HYDROLYZABLE METALLOSILOXANE IS PROVIDED AND THERE IS INCORPORATED THEREIN LEAD OXIDE AND, WHEN PRESENT, ZINC OXIDE, TO FORM IN THE CLEAR SOLUTION A UNIFORM DISPERSION OF THESE OXIDES, AFTER WHICH THE SYSTEM IS FURTHER HYDROLYZED SO AS TO FORM A UNIFORM GEL AND THE GEL IS APPROPRIALTELY HEATED AND CALCINED TO PRODUCE SUBSTANTIALLY A CARBON-FREE, INORGANIC GLASS PRECURSOR WHICH, UPON FURTHER HEATING, FROMS A COLORLESS GLASS.

United States Patent Otfice 3,799,754 Patented Mar. 26, 1974 3,799,754METHOD FOR PRODUCING GLASS PRECURSOR COMPOSITIONS AND GLASS COMPOSITIONSTHEREFROM Ian M. Thomas, Temperance, Mich., assignor to Owens-Illinois,Inc. No Drawing. Filed Nov. 27, 1972, Ser. No. 309,946 Int. Cl. C03b5/16; C08h 1/34 US. Cl. 65-434 23 Claims ABSTRACT OF THE DISCLOSURE Animproved process for preparing inorganic, oxidic, glass precursorcompositions correspondingto a glass consisting essentially of silica,boric oxide, lead oxide, and, optionally, alumina or zinc oxide ormixtures of alumina and zinc oxide, wherein the glass has a sinteringtemperature in the range of about 300 C. to about 600 C. and melts to auniform glass product at a temperature of less than about 860 C. by aprocess wherein a clear solution of a further hydrolyzablemetallosiloxane is provided and there is incorporated therein lead oxideand, when present, zinc oxide, to form in the clear solution a uniformdispersion of these oxides, after which the system is further hydrolyzedso as to form a uniform gel and the gel is appropriately heated andcalcined to produce substantially a carbon-free, inorganic glass precursor which, upon further heating, forms a colorless glass.

THE INVENTION The present invention is directed to a method for forminginorganic, oxidic, glass precursor compositions and the manufacture ofglasses therefrom.

In US. Pat. No. 3,640,093, which is hereby incorporated by reference,there is described a process for forming oxidic products, and glassesfrom these oxidic products, by a process wherein certain siliconalkoxides are combined and reacted with a sufficient quantity of waterin the presence of an effective catalytic amount of an inorganic acidhydrolysis catalyst so as to form a clear solution of a soluble,partially hydrolyzed silicon alkoxide, the amount of water used forhydrolysis being insufficient to cause precipitation in said solutionupon the subsequent addition of an alkoxide thereto, and then this clearsolution is reacted with a metal alkoxide so as to form a clear solutionof a soluble, further hydrolyzable metallosiloxane; the latter clearsolution can then be combined and reacted with an aqueous solution of ametal salt that decomposes to an oxide and thereby provides a systemcontaining the needed oxides, as precursors, for the glass compositionin a homogeneous solution form after which time this solution, in thepresence of an effective gelling amount of water, is gelled and the geldried and heated to obtain an oxidic product therefrom. The preferredmetal salts are acetates because other" salts, for example, thenitrates, have high decomposition points and represent a potentialexplosion hazard when employed on a large scale and others also havehigh decomposition points relative to the acetate.

In preparing oxidic, glass precursor compositions by the use of Si('OR)and alkoxides and acetates in the technique disclosed therein, whereinthe composition corresponds to a glass consisting essentially of SiO B 0PhD, and, optionally, A10 or ZnO, or mixtures of A1 0 and ZnO, andwherein the glass has a sintering temperature in the range of about 300C. to about 600 C. and melts to a uniform glass product at a temperatureless than about 860 C., a problem has been observed. The problem alsoexists in making a glass from the precursor. That is, when manufacturingprecursors of the type indicated above, with their low sinteringtemperatures and low melting temperatures, it has been observed that theprecursor which is produced by heating of the gel, as set forth in thatpatent, is black and it is very ditlicult and time consuming to producea non-sintered, non-black, granular or particulate precursor by heatingbelow the sintering temperature of these compositions. If highertemperatures are used, it is found that the glass formed from theprecursor is black unless heated for prolonged periods at a temperaturewell above the melting temperature of the composition. This isunsatisfactory when one considers that the precursor compositionsgenerally correspond to glasses used for passivation purposes, forsealing purposes, or as binders for noble or other metals, like copper,such as in the application, and formation, of thick films formicroelectronic purposes. It will be appreciated that the utility of theglasses in these areas is largely predicated on their ability to formfilms of uniform, homogeneous, high quality glass in a very short periodof time. The blackening problem in the precursor and in the glass isindicative of a non-uniform, non-homogeneous low quality composition notwell suited for the intended usages. Likewise, the prolonged heatingperiods, above the melting temperature to eliminate this, detracts fromthe economy and efliciency of the end use process. What is needed is aprocess for forming a substantially carbon-free, inorganic oxide, glassprecursor which, when used as intended, for example, as a binder fornoble, or other metals, like copper, in thick film microelectronicapplications, can be easily converted to a homogeneous, uniform,colorless (i.e., nonblack) glass in the shortest possible time with theleast expenditure of energy.

Since the precursor compositions sinter between about 300 C. and about600 C., it is likely that sintering occurs at a temperature lower thanthat needed to burn out acetate residues and this sintering limits theavailability of oxygen or air needed for burnout of carbon moieties. Itis also likely that in heating the gel to remove acetate residues, areducing atmosphere tends to form and results in the formation ofsubstantial amounts of free lead, and zinc when present, which requiressubstantial later additional heating to oxidize them back into the oxidestate. Whatever the reason for the problem, it has now beensubstantially solved and the needed process provided.

Applicant has now devised a method for forming the needed precursors ofthe composition corresponding to a glass consisting essentially of SiO B0 PhD, and, optionally, A1 0 or ZnO, or mixtures of A1 0 and ZnO,wherein the glass has a sintering temperature in the range of about 300C. to about 600 C. and melts to a uniform glass product at a temperatureless than 860 C. wherein the inorganic, oxidic, glass precursor can beformed as a granular or particulate material which is substantiallycarbon-free and free of any black coloration and wherein, when thisprecursor is heated, it is easily and conveniently converted to asubstantially colorless glass. For convenience, the term precursor isused because in actual use, these inorganic oxidic materials will beheated above their melting temperature to get them to flow into auniform, unitary shape, e.g., as a thick film on microelectronicapplications. The products, however, which are designated precursors,may be considered glasses themselves. The problem is solved and the needis satisfied by eliminating the use of acetates in the process of US.Pat. No. 3,640,093, and supplying the needed PhD and, when present ZnO,in the form of particulate lead oxide and zinc oxide. As used herein,lead oxide and zinc oxide include both anhydrous forms and hydratedforms.

Thus, in accordance with one feature of this invention, there isprovided a process for preparing an inorganic oxidic, glass precursorcomposition corresponding to a glass consisting essentially of silica,boric oxide, lead oxide, and, optionally, alumina or zinc oxide, ormixtures of alumina and zinc oxide, wherein the glass has a sinteringtemperature in the range of about 300 C. to about 600 C. and melts to auniform glass product at a temperature less than about 860 C., saidmethod comprising the steps of:

(I) combining Si(OR) wherein R is an alkyl of 1 to 6 carbon atoms with asufficient quantity of water and in the presence of an effectivecatalytic amount of an inorganic acid hydrolysis catalyst so as to forma clear solution of a soluble, partially hydrolyzed silicon alkoxide,wherein the amount of water is insuflicient to cause precipitation insaid solution upon the addition of boron alkoxide or aluminum alkoxidethereto,

(II) reacting said clear solution of a soluble partially hydrolyzedsilicon alkoxide with boron alkoxide and, when A1 is also present,aluminum alkoxide, so as to form a clear solution of a soluble, furtherhydrolyzable metallosiloxane,

(III) adding in any of said steps (I) or (II), or subsequent thereto,lead oxide and, when ZnO is present, zinc oxide, so as to form in saidclear solution of a soluble, further hydrolyzable metallosiloxane auniform dispersion of lead oxide and, when present, zinc oxide,

(IV) further hydrolyzing said further hydrolyzable metallosiloxane inthe presence of an effective gelling amount of water so as to convertsaid clear solution of a soluble, further hydrolyzable metallosiloxanecontaining said dispersed lead oxide and, when present, zinc oxide, intoa uniform gel structure, and

(V) heating said gel structure for a time and at a temperaturesufficient to convert said gel to a substantially carbon-free, inorganicoxide product.

The heating can be done to effect the formation of the substantiallycarbon-free oxide product at temperatures which are below the sinteringtemperature of the composition and thereby result in the formation of aparticulate or generally granular product. This product may then beemployed for its intended use, such as, for example, by being combinedwith noble or other metals like copper, for purposes ofacting as abinder and applied as a thick film on substrates, and then easily andconveniently converted to a colorless, molten glass with the amount ofenergy being required to obtain this molten glass now being greatlydecreased relative to the former use of acetates. Since the precursorcomposition will consist of glass forming oxides, all that is requiredis that the precursor then be heated to the appropriate temperature fora sufficient time to convert the precursor into a colorless, thaat is,non-black or black-gray, uniform, homogeneous, molten glass.

According to another feature of this invention, there is provided aprocess for preparing an inorganic oxide glass precursor compositioncorresponding to a glass consisting essentially of silica, alumina,boric oxide and lead oxide, and wherein said glass has a sinteringtemperature in the range of about 300 C. to about 600 C. and melts to auniform glass product at a temperature less than about 860 C., saidmethod comprising the steps of:

(I) combining Si(OR) wherein R is an alkyl of 1 to 6 carbon atoms with asufficient quantity of water and in the presence of an effectivecatalytic amount of an inorganic acid hydrolysis catalyst 50 as to forma clear solution of a soluble, partially hydrolyzed silicon alkoxide,wherein the amount of water is insufiicient to cause precipitation insaid solution upon the addition of boron alkoxide and aluminum alkoxidethereto,

(II) reacting said clear solution of a soluble, partially hydrolyzedsilicon alkoxide with aluminum alkoxide so as to form a clear solutionof a soluble, further hydrolyzable alum nosiloxane,

(III) adding in any of step (I) or (II), or subsequent thereto, leadoxide and boron alkoxide so as to form a clear solution of a soluble,further hydrolyzable aluminoborosiloxane containing a uniform dispersionof lead oxide,

(IV) further hydrolyzing said further hydrolyzable aluminoborosiloxanein the presence of an effective gelling amount of water so as to convertsaid clear solution of a soluble, further hydrolyzable,aluminoborosiloxane containing said dispersed lead oxide into a uniformgel structure, and

(V) heating said gel structure for a time and at a temperaturesufficient to convert said gel to a substantially carbon-free, inorganicoxide product.

Yet, according to another feature of this invention, there is provided aprocess for preparing an inorganic oxide, glass precursor compositioncorresponding to a glass consisting essentially of silica, B 0 and PbO,and wherein the glass has a sintering temperature in the range of about300 C. to 600 C. and melts to a uniform glass product at a temperatureless than about 860 C., said method comprising the steps of:

(I) combining Si(OR) wherein R is an alkyl of 1 to 6 carbon atoms with asufficient quantity of water and in the presence of an effectivecatalytic amount of an inorganic acid hydrolysis catalyst so as to forma clear solution of a soluble, partially hydrolyzed silicon alkoxide,wherein the amount of water is insufficient to cause a precipitation insaid solution upon the addition of boron alkoxide thereto,

(II) reacting said clear solution of a soluble, partially hydrolyzedsilicon alkoxide with boron alkoxide so as to form a clear solution of asoluble, further-hydrolyzable borosiloxane,

(III) adding lead oxide in any of step (I) or (II) or subsequent theretoso as to form a clear solution of a soluble, further hydrolyzableborosiloxane containing a uniform dispersion of said lead oxide,

(IV) further hydrolyzing said further hydrolyzable borosiloxane with aneffective gelling amount of water so as to convert said clear solutionof a soluble, further hydrolyzable borosiloxane containing saiddispersed lead oxide into a uniform gel structure, and

(V) heating said gel structure for a time and at a temperaturesufficient to convert said gel to a substantially carbon-free, inorganicoxide product.

As used herein, sintering temperature contemplates that temperature atwhich particulate glass flows sufficiently, presumably on its surface,to begin to bind adjacent particles together but yet insufficient toform a molten mass. The term colorless glass contemplates the formationof a glass having no residual black or blackish-gray coloration andwould thus comprehend glasses having a certain degree of coloration suchas, for example, light yellow, but which do not include black orblackish-gray coloration. The term aluminum alkoxide contemplatescompounds of the formula Al(OR') wherein R is an alkyl of 1 to 6 carbonatoms The term aluminum alkoxide also comprehends the inclusion ofso-called double metal alkoxides of the formula MAl (OR') wherein M isan alkaline earth metal such as, for example, magnesium or calcium ormixtures of the compounds of the two formulae set forth. Thus, whensmall amounts of magnesium or calcium are desired to be incorporated inthe glass, they may be added in the form of the double alkoxide. Theterm boron alkoxide contemplates compounds of the formula B(OR) whereinR is an alkyl of 1 to 6 carbon atoms. Highly preferred alkoxides arealuminum butoxide, for example, aluminum secondary butoxide and methylborate.

The inorganic oxidic glass precursor composition will be routinelyselected by those skilled in the art and will correspond to glasscompositions consisting essentially of silica, B 0 lead oxide, and,optionally, A1 0 or ZnO, or

mixtures of A1 and ZnO, and wherein said glass has a sinteringtemperature'in the range of about 300 C. to about 600 C. and melts to auniform glass product at temperatures less than about 860 C. Exemplarycompositions include compositions consisting essentially of about 5 to26 weight percent PbO, 41 to about 62 weight percent ZnO, 12 to about 23weight percent SiOg, and 11 to about 21 weight percent B 0 Othersinclude compositions of about 2 to 7 percent PbO, 12 to 25 percent B 055 to 64 percent ZnO, 9 to 18 percent SiO and 1 to 5 percent A1 0 Othercompositions will be routinely selected by those skilled in the art. Itwill also be appreciated that other metal oxides may be included insmall quantities; those other oxides if added, however, will be added asthe alkoxide of the metal or as a particulate metal oxide. Especiallyuseful, high quality products are obtained when using compositions inapproximate weight percent on a theoretical oxide basis of about 5 to 30percent B O about 5 to 30 percent SiO and about 40 to 90 percent PbO,and especially compositions in the range wherein the ratio of B 0 to Si0is about 1:1, for example, a composition consisting essentially of about13.5 weight percent B 0 about 13.5 weight percent SiO and 73 Weightpercent PbO. An especially highly desirable and useful composition whichis manufactured in accordance with this invention is a compositionconsisting essentially of, on a theoretical oxide basis, in approximateweight percent of 40 to 80 percent PbO, 4 to 12 percent A1 0 16 to 18percent B 0 and to 30 percent SiO Especially suitable glasses will be inthe ranges indicated above, for example, 4-12 percent A1 0 and whereinthe ratio of A1 0 to B 0 to SiO is about I to 1.5 to 2.5. Exemplary ofsuch a highly suitable composition is one consisting essentially ofabout 65 percent PbO, about 7 percent A1 0 about 10.5 percent B 0 andabout 17.5 percent SiO The hydrolysis of the tetra-alkoxy silane orsilicon a1- koxide, Si(OR) to form a clear solution of a partiallyhydrolyzed and probably partially condensed silicon alkoxide isadvantageously done in the persence of an organic solvent, the solventbeing present in an amount sufiicient to maintain the partiallyhydrolyzed silicon alkoxide in solution and also to maintain a solutionof the subsequently formed aluminosiloxane, borosiloxane oraluiminoborosiloxane composition, as the case may be. Suitable organicsolvents will be relatively volatile solvents, for example, organicsolvents havin boiling points below about 200 C. and, preferably, belowabout 150 C. C -C alkanols are suitable with C to C alkanols beinghighly preferred. Ethanol is most preferred. The amount of solvent willbe routinely selected by those skilled in the art but, generally, anamount between about one-half to about an equal volume of Si(OR) will befound quite suitable. Additionally, the hydrolysis is effected in thepresence of an effective catalytic amount of an inorganic acidhydrolysis catalyst such as, for example, mineral acids, like HCl, andalso including the Lewis acids. The amount will be routinely selected bythose skilled in the art and quite convenient operation will be obtainedat pHs in the range of about 2 or 2.5 to about 5. The amount of Waterinitially employed to effect the formation of the partially hydrloyzedsilicon alkoxide should not be of a quantity such as to causeprecipitation or gellation upon the subsequent addition of boronalkoxide or aluminum alkoxide, or mixtures thereof, to the clearsolution of the soluble, partially hydrolyzed silicon alkoxide. It isdesired in this regard to subsequently form a clear solution for afurther hydrolyzable metallosiloxane, e.g. borosiloxane,aluminosiloxane, or alumino-borosiloxane, e.g. borosiloxane,aluminosiloxane, or alumino-borosiloxane as the case may be, so as tohave the glass forming oxides provided by these metals in thehomogeneous relationship provided by the solution. Precipitation, forexample on the addition of the aluminum alkoxide, results innon-homogeneity. Usually, the minimum amount of water to effect thedesired partial hydrolysis will be about .3 equivalent (mole) of waterper equivalent (mole) of silicon alkoxide. When alumina is to be presentin the composition, the amount of water employed will generally bebetween about 3 and about 1.5 equivalents (moles) per equivalent (mole)of silicon alkoxide. Quite suitable results will be obtained usingaluminum alkoxide to provide alumina by using approximately 1 equivalentof water per equivalent of silicon alkoxide. When alumina is not to bepresent in the composition and the composition con sists essentially ofsilica, B 0 lead oxide, and, optionally, zinc oxide, slightly higheramounts of Water may be employed, for example, up to 2 or 3 equivalentsof water per equivalent of silicon alkoxide.

As indicated in U.S. Pat. 3,640,093, the metal alkoxide, for example,boron alkoxide or aluminum alkoxide, or both, are then reacted with theclear solution of a soluble, partially hydrolized silicon alkoxide so asto form a clear solution of a soluble, further hydrolyzablemetallosiloxane, which metallosiloxane, depending on the composition,may be a borosiloxane, an aluminosiloxane, or an aluminoborosiloxane.

The lead oxide and, when included zinc oxide, can be added to thereaction system in the step for hydrolyzing the silicon alkoxide or inthe step wherein the aluminum alkoxide, boron alkoxide, or both, areadded to the partially hydrolyzed silicon alkoxide solution to form thefurther hydrolyzable metallosiloxane, or subsequent to these steps. Theimportant consideration is that the lead oxide and, when present, zincoxide, be uniformly dispersed in the clear solution of the soluble,further hydrolyzable metallosiloxane, for example, aluminoborosiloxane,prior to gelling that solution so that when gellation occurs, the oxidewill be uniformly dispersed in the gel. The oxides employed will beparticulate materials, preferably minus about 400 mesh and, mostdesirably, will, have a particle size less than. 10 microns.Commercially available powders having a size distribution of about 1 to5 microns produce excellent results. In manufacturing, for example, alead aluminoborosilicate, it will be convenient to first add thealuminum alkoxide to the clear solution of the partially hydrolizedsilicon alkoxide, forming a further hydrolyzable aluminosiloxanesolution, then adding the methyl borate, forming -a further hydrolyzablealuminoborosiloxane, followed by the addition of the lead oxide. Otherorders as hereinbefore set forth may be employed, with the importantconsideration being the formation of a clear solution of a soluble,further hydrolyzable metallosiloxane containing a uniform dispersion oflead oxide, and zinc oxide when present.

After a uniform dispersion of the lead oxide and, when present, zincoxide is formed in the clear solution of the soluble, furtherhydrolyzable metallosiloxane, the solution is gelled in the presence ofan elfective gelling amount of water. This may be done by adding anadditional quantity of water to further hydrolyze the furtherhydrolyzable metallosiloxane, resulting in further hydrolysis,condensation and cross-linking, and the production of the gel. Theamount of water which is totally employed in the reaction method,including that used in the initial hydrolysis of silicon alkoxide, andwhich will be found to be effective in forming the gel, is generally anamount theoretically required to react with all of the individual 0Rgroups added as the reactants. For example, for each mole oftetra-alkoxy silane that was used, four moles of total water will beneeded to calculate the total amount of 'water which will be effectivein gelation and, likewise, for each mole, for example, of aluminumalkoxide, three moles of water will be required. Slight excesses areusually preferred. The water, except for that which has been used in thestep for hydrolyzing the silicon alkoxide, will be conveniently addedafter all the ingredients have been added into the reaction system,although, if desired, for convenience, a portion of the water may, forexample, be added to the metallosiloxane before lead oxide, and zincoxide when present, are added, provided these oxides are incorporated inthat solution in a uniform manner before gelation begins.

After formation of the gel, the gel is heated in air or oxygen to removefree liquid components such as, for example, any excess water which maybe present, the solvent used, and alkanol by-product, and then thisproduct is further heated to remove carbonaceous residues which may bepresent in the form of bound alkanol and unreacted alkoxide groups,notwithstanding the fact that theoretically suflicient water has beenadded to react with them. Drying of the gel produces a very friable massand upon heating to remove carbonaceous residues, a particulate orgenerally granular material is obtained. Thus, for example, the gel maybe heated for a sufiicient period of time at a temperature of around 100to 110 C. to dry same and then the temperature gradually raised up toabout, for example, 300 C. or at a temperature less than the sinteringtemperature of the composition involved so as to form a generallygranular, carbon-free, oxidic precursor consisting of glass formingoxides. This product may then be converted to a glass such as, forexample, glass coating, by applying it either as a binder with othermaterials, or alone, onto an appropriate substrate and then heating thesubstrate to a temperature and time sufficient to convert it into auniform, colorless glass. Darkening may initially result upon heating ofthe precursor to a glass but this is easily removed by heating to aslightly higher temperature or by heating for a slightly longer time.

While the foregoing describes the present invention with sufficientparticularity to enable those skilled in the art to make and use sameand includes the best mode contemplated in practicing the invention,several examples follow. These examples further illustrate the presentinvention.

'EXAMPLE 1 An oxidic product, and from this, a colorless glass, of theapproximate compoosition 13.5 percent SiO 13.5 percent B and Y73 percentPbO is prepared as follows. About 46.9 grams of distilled ethyl silicateare dissolved in about 33 ml. of ethanol and there are then added about4 ml. of water (about 1 equivalent of water per equivalent of ethylsilicate) and 2 drops of 1 normal HCl. The solution is then heated toabout 60 C. to enhance the rate of hydrolysis and results in theformation of a visually clear solution of a soluble, partiallyhydrolyzed ethyl silicate. This solution is then cooled to about 30 C.and about 40.2 g. of methyl borate are added, resulting in the formationof a visually clear solution of a soluble, partially hydrolyzed metallo(boro) siloxane. To this clear solution there are then added about 73grams of particulate PbO of 99.9 percent purity and having a particlesize in the range of about 1 to 5 microns. The mixture is thenvigorously agitated, in this case by means of a conventional ultrasonicagitating device, so as to form in the clear solution of the soluble,further hydrolyzable borosiloxane a uniform dispersion of the leadoxide. 60 ml. of water are then added to the mixture while continuingagitation and the mixture then allowed to gel. The gel is then broken upand dried in an air oven overnight at about 110 C. so as to remove freeliquid components, for example, water and ethanol (both the solvent andby-product) and is then heated to about 300 C. and held there for abouttwo and one-half hours to remove residual carbon moieties, such as, forexample, residual alkoxy groups and probably some bound ethanol. A paleyellow, substantially carbon-free, granular, inorganic oxide product isobtained.

A sample of the above product is then heated in a crucible and melts andfuses to a dark glass at about 600 to 650 C. This dark glass becomesclear on further heat ing to 800 C.

By repeating the above procedure but, in lieu of lead oxide, using leadacetate to provide the needed lead oxide, a clear, colorless glass isnot obtained at 800 C. even when heated longer than the materialproduced by using lead oxide.

EXAMPLE 2 A substantially carbon-free, inorganic oxide productcorresponding to a glass composition on a theoretical oxide basis, ofabout 17.5 weight percent SiO 7 weight percent A1 0 10.5 weight percentB 0 and 65.0 weight percent PbO, is prepared as follows. Into about 425ml. of commercially available proprietary ethanol solvent (whichcontains about 17 grams of water) there are charged 607 grams ofdistilled ethyl silicate, 35.5 grams of distilled water, and 24 drops of1 normal nitric acid. The ingredients are stirred and heated to 60 C. toassist in the hydrolysis reaction and results in the formation of aclear solution of a soluble, partially hydrolyzed ethyl silicate. Thereare then added to the clear solution about ml. of secondary butanol andabout 338 grams of aluminum secondary butoxide in 4 increments withstirring so as to maintain a clear solution. The temperature rises toabout 65 C., resulting in the formation of a clear solution of asoluble, further hydrolyzable aluminosiloxane. The latter clear solutionis then allowed to cool to about 30 C. and about 650 grams of PbO(Fisher L71) are added with vigorous mechanical stirring, so as to formin the clear solution of the soluble, further hydrolyzablealuminosiloxane a uniform dispersion of lead oxide therein. About 81grams of water, which is about one-half the water needed totheoretically hydrolyze the charge of methyl borate, are then added withstirring and serve to further hydrolyze the further hydrolyzablealuminosiloxane. There are then added about 313 grams of methyl boratewith agitation, thereby forming a clear solution containing analuminoborosiloxane, having uniformly dispersed therein the lead oxide.About 314 grams of water are then added to further hydrolyze the furtherhydrolyzable aluminoborosiloxane and after about five minutes, the clearsolution containing the uniform dispersion of lead oxide forms auniform, homogeneous gel. The total charge of water in this reaction isabout 447.5 grams or about 24.85 moles which corresponds to the amountof water theoretically required to react with each of the individualalkoxide groups added in the form of ethyl silicate, aluminum butoxideand methyl borate. The firm gel is transferred to a large Teflon trayand heated at about 60 C. for approximately 18 hours. This effects apartial volatilization of some of the liquid components, for example,alkanol byproduct, the solvent, and the secondary butanol added. Theproduct, an extremely friable granular material, is then crushed to anextremely fine particle size, orange-colored powder. The powder is thenheated for approximately one and one-quarter hours at 100 0., one andone-quarter hours at 0., two hours at 200 C., two hours at 250 C., andabout 17 hours at 300 C. so as to remove by heating residual volatilesand carbon moieties which may be present in the form of residualunreacted alkoxide groups or in the form of bound alcohol. A generallyyellow-colored, substantially carbon-free, non-sintered, inorganic oxideproduct results.

This product is then deposited, in about a 5 to 10 mil thickness, ontoan alumina substrate, and the coated substrate is then subjected in airto different temperature gradients for a period of approximatelyone-half hour, the temperature ranging generally from about 585 C. toabout 920950 C. After being heated for about onehalf hour, it isobserved that a grayish-black glass results up to a temperature of about660 C.-700 C. and that at temperatures above this point, there results asmooth, glossy, uniform film of colorless glass. It is believed that asubstantial cause of the early grayish-black coloration may be theresult of elemental lead being present, which lead is oxidized uponfurther heating at the higher temperatures.

EXAMPLE 3 In a like manner, a non-sintered, substantially carbonfree,inorganic oxide product is produced with the amount of ethyl silicate,aluminum butoxide, methyl borate and lead oxide being selected so as toproduce a composition on a theoretical oxide basis corresponding to aglass consisting of about 60 weight percent PbO, 20 weight percent SiO 8weight percent A1 and 12 weight percent B 0 Upon being subjected to thetemperature gradients, as set forth in Example 2, it is observed thatthe powder initially sintered at a temperature less than 600 C. and thatup to a temperature of about 620 to 635 C., there is a matty, sinteredgrayish-black mass. Above this temperature, and up to a temperature ofabout 740 to 750 C., it is observed that the coating is a glossy,uniform glass having a blackish-gray color. Above the latter temperature, it is observed that the glass is uniform, glossy andcolorless.

Substantially similar case in producing a colorless, i.e., no black orblackish-gray coloration, glass with compositions containing zinc oxide,in addition to lead oxide, results by adding the requisite amount of thezinc oxide, along with the lead oxide as hereinabove indicated.

I claim:

1. A process for preparing an inorganic, oxidic glass precursorcomposition corresponding to a glass consisting essentially of silica, B0 PhD and, optionally, A1 0 or ZnO or mixtures of A1 0 and ZnO, whereinsaid glass has a sintering temperature in the range of about 300 C. toabout 600 C. and melts to a uniform glass product at a temperature lessthan about 860 C., said method comprising the steps of:

(I) combining Si(OR) wherein R is an alkyl of 1 to 6 carbon atoms with asuflicient quantity of water and in the presence of an effectivecatalytic amount of an inorganic acid hydrolysis catalyst so as to forma clear solution of a soluble, partially hydrolyzed silicon alkoxide,wherein the amount of water is insufficient to cause precipitation insaid solution upon the addition of boron alkoxide or aluminum alkoxidethereto,

(II) reacting said clear solution of a soluble, partially hydrolyzedsilicon alkoxide with boron alkoxide and, when A1 0 is also present,aluminum alkoxide so as to form a clear solution of a soluble, furtherhydrolyzable metallosiloxane,

(III) adding in any of said step (I) or (II), or subsequent thereto,lead oxide and, when ZnO is present, zinc oxide, so as to form in saidclear solution of a soluble, further hydrolyzable metallosiloxane auniform dispersion of lead oxide and, when present, zinc oxide,

(IV) further hydrolyzing said further hydrolyzable metallosiloxane inthe presence of an effective gelling amount of water so as to convertsaid clear solution of a soluble, further hydrolyzable metallosiloxanecontaining said dispersed lead oxide and, when present, zinc oxide, intoa uniform gel structure, and

(V) heating said gel structure for a time and at a temperaturesufficient to convert said gel to a substantially carbon-free, inorganicoxide product.

2. The method of claim 1 wherein said composition corresponding to aglass having a sintering temperature in the range of about 300 C. toabout 600 C. and which melts to a uniform, glass product at atemperature less than about 860 C. consists essentially of, inapproximate weight percent, 40 to 80 percent PbO, 4 to 12 percent A1 0 6to 18 percent B 0 and .10 to 30 percent SiO 3. The method of claim 2 andfurther including the step of heating said inorganic oxide compositionat a temperature and for a time suflicient for said material to flowinto a uniform, colorless glass.

4. The method of claim 2 wherein Si(OR)., is ethyl silicate, saidaluminum alkoxide is aluminum butoxide and said boron alkoxide is methylborate.

5. The method of claim 2. and wherein the weight percent ratio of A1 0to B 0 to SiO is about 1 to 1.5 to 2.5.

6. The method of claim 5 wherein said composition consists essentiallyof about 65 percent PbO, about 7 percent A1 0 about 10.5 percent B 0 andabout 17.5 percent SiO 7. The method of claim 1 wherein said compositioncorresponding to said glass having a sintering temperature in the rangeof about 300 C. to about 600 C. and which melts to a uniform, glassyproduct at a temperature less than about 860 C. consists essentially of,in approximate weight percent, 5 to 30 percent B 0 5 to 30 percent SiOand 40 to 90 percent PbO.

8. The method of claim 7 and. further including the step of heating saidinorganic oxide composition at a temperature and for a time suflicientfor said material to flow into a uniform, colorless glass.

9. The method of claim 8' wherein the weight percent ratio of B Og toSiO is about 1:1.

10. The method of claim '8 wherein said composition in approximateweight percent is 13.5 percent B 0 13.5 percent SiO and 73 percent PbO.

11. The process for preparing an inorganic oxide glass precursorcomposition corresponding to a glass consisting essentially of silica,alumina, boric oxide and lead oxide and wherein said glass has asintering temperature in the range of about 300 C. to about 600 C. andmelts to a uniform glass product at a temperature less than about 860C., said method comprising the steps of:

(I) combining Si(OR)., wherein R is an alkyl of 1 to 6 carbon atoms witha suflicient quantity of water and in the presence of an effectivecatalytic amount of an inorganic acid hydrolysis catalyst so as to forma clear solution of a soluble, partially hydrolyzed silicon alkoxide,wherein the amount of water is insufiicient to cause precipitation insaid solution upon the addition of boron alkoxide and aluminum alkoxidethereto,

(11) reacting said clear solution of a soluble, partially hydrolyzedsilicon alkoxide with aluminum alkoxide so as to form a clear solutionof a soluble, further hydrolyzable aluminosiloxane,

(III) adding in any of step (I) or (II), or subsequent thereto, leadoxide and boron alkoxide, so as to form a clear solution of a soluble,further hydrolyzable alurninoborosiloxane containing a uniformdispersion of lead oxide,

(*IV) further hydrolyzing said further hydrolyzable aluminosiloxane inthe presence of an effective gelling amount of water so as to convertsaid clear solution of a soluble, further hydrolyzablealuminoborosiloxane containing said dispersed lead oxide into a uniformgel structure, and

(V) heating said gel structure for a time and at a time and at atemperature sufficient to convert said gel to a substantiallycarbon-free, inorganic oxide product.

12. The method of claim 11 wherein the amount of Water used in step (I)is between about 0.3 and about 1.5 equivalents of water per equivalentof Si(OR) and wherein step I is performed in the presence of a C to Calcohol.

13. The method of claim 12 wherein the percentages of said oxides areapproximately in the range of 40 to weight percent PbO, 4 to 12 weightpercent A1 0 6 to 18 weight percent B 0 and 10 to 30 weight percent Si014. The method of claim 13 wherein said composition is approximately 65weight percent PbO, 7 weight percent A1 0 10.5 weight percent B 0 and17.5 weight percent SiO 15. The method of claim 13 wherein alumina ispresent in the range of about 4 to 12 percent and wherein the weightpercent ratio of A1 to B 0 to SiO is about 1 to 1.5 to 2.5.

16. The method of claim wherein Si(OR) is ethyl silicate.

17. The method of claim 16 wherein said boron alkoxide is methyl borateand wherein said aluminum alkoxide is an aluminum butoxide.

18. The method of claim 13 and further including the step of heatingsaid inorganic oxide material at a temperature and for a time suflicientfor said material to flow into a uniform colorless glass.

19. A process for preparing an inorganic oxide glass precursorcomposition corresponding to a glass consisting essentially of SiO B 0and PbO and wherein said glass has a sintering temperature in the rangeof about 300 C. to about 600 C. and melts to a uniform, glass product ata temperature less than about 860 C., said method comprising the stepsof:

(-I) combining Si(OR) wherein R is an alkyl of 1 to 6 carbon atoms witha sufiicient quantity of water and in the presence of an effectivecatalytic amount of an inorganic acid hydrolysis catalyst so as to forma clear solution of a soluble, partially hydrolyzed silicon alkoxide,wherein the amount of water is insufficient to cause a precipitation insaid solution upon the addition of boron alkoxide,

(II) reacting said clear solution of a soluble, partially hydrolyzedsilicon alkoxide with boron alkoxide so as to form a clear solution of asoluble, further hydrolyzable borosiloxane,

(HI) adding lead oxide in any of step (I) or (II), or subsequentthereto, so as to form a clear solution of a soluble, furtherhydrolyzable borosiloxane containing a uniform dispersion of said leadoxide,

(IV) further hydrolyzing said further hydrolyzable aluminosiloxane withan effective gelling amount of water so as to convert said clearsolution of a soluble, further hydrolyzable borosiloxane containing saiddispersed lead oxide into a uniform gel structure, and

(V) heating said gel structure for a time and at a temperaturesufficient to convert said gel to a substantially carbon-free, inorganicoxide product.

20. The method of claim 19 wherein the approximate weight percent ofsaid oxides in said composition is as follows: 5 to 30 percent B 0 5 to30 percent S102, and 40 to percent PbO.

21. The method of claim 20 wherein said composition is approximately13.5 percent B 0 13.5 percent $0,, and 73 percent PbO.

22. The method of claim 20 and further including the step of heatingsaid inorganic oxide at a temperature and for a time sufiicient for saidmaterial to flow into a uniform colorless glass.

23. The method of claim 22 wherein the amount of Water employed in step(I) is about 1 equivalent of water per equivalent of silicon alkoxide,said silicon alkoxide is ethyl silicate and wherein step (I) isperformed in the presence of a C to C alcohol.

References Cited UNITED STATES PATENTS 3,313,737 4/1967 Brimsmead et al.106-3835 X 3,640,093 2/1972 Levene et al. 65-134 3,678,144 7/1972 Shoup106-3835 X 3,690,366 9/ 1972 Schwartz 106-3835 X FOREIGN PATENTS 768,45512/ 1971 Belgium.

OTHER REFERENCES Vol. 39, Journal of the American Ceramic Soc., pp.-146, by Rustum Roy.

Vol. 52, N0. 6, Journal of the American Ceramic Soc., p. 344, by RustumRoy.

ROBERT L. LINDSAY, 111., Primary Examiner US. Cl. X.R. 10638.35, 53, 54

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent 5 freer/6Dated March 26, 1974 Inventor(s) Ian M. Thomas It is certified thaterror appears in the above-identified patent and that said LettersPatent are hereby corrected as shown below:

Column 1, line 67, "A103" should be A1203 Column 5, line 5, "thaet"should be that Column 4, line 55, "step" should be steps Column 5, line14, "those" should be these Column 5, line 62, "hydrloyzed should behydrolyzed Celurnn 5, line 68, "for" should be of Column 5, lines 70-71,delete "e.g. borosiloxane, eluminosiloxane, or alumino-borosiloxane".

Column 6, line 5, "5" should be .5

Column 7,; line 41, "compoosition" should be composition cilsim 1.,column 9, line 50, "step" should be steps Cl a, 1m ll, column 10, line47 "step" should be steps Claim ll, column 10, line 59 delete "time andat a" 1 Claim 19, column ll, line 35, "step" should be steps Signed andsealed this 17th day of September 19/4.

(SEAL) Attest:

McoOY M, slDsoN JRm G. MARSHALL DANN Attestlng officer Commlssioner ofratents ORM O-1050 (10-69) USCOMM-DC 60376-F69 Iv u 5 GOVERNMENTPRINTING OFFICE: I969 0-366-334,

